Communication using the UWB is a communication method utilizing 20% of a central frequency or a band of 500 MHz or more which is a remarkably wide band ranging from several hundreds of megahertzes to several gigahertzes. Since an output is lower than a noise level of a personal computer, the communication method has various advantages such as capability of sharing with a currently used frequency, capability of high speed communication, applicable to positioning and distance measurement, and simple structure of impulse type circuit without using a carrier wave. Therefore, use of the communication method is expected to be expanded in various fields in near future.
Since the UWB uses the considerably wide band, an antenna using an ultrawideband that has not been utilized in the art, such as that having a full band of 3.1 to 10.6 GHz, a high band of 5 to 10.6 GHz, and a low band of 3.1 to 5 GHz, is required. Such ultrawideband antenna is disclosed in a reference 1 and reference 2.    [Reference 1] Technical Information Magazine “FIND” (vol. 23, No. 1); pages 32 to 35; published on January, 2005 by Fujitsu Kabushiki Kaisha Electronic Device Division.    [Reference 2] JP-A-2002-217897
Since the ultrawideband antenna disclosed on page 35 of the reference 1 and the ultrawideband antenna disclosed in paragraphs [0065] to [0069] and FIGS. 22 and 23 of the reference 2 are flat antenna type, these ultrawideband antennas are not sufficiently downsized though they are reduced in thickness, thereby raising a drawback of limited application. For example, the flat ultrawideband antenna disclosed on page 35 of reference 1 requires a length and a width of 30 mm×40 mm.
As a countermeasure for such drawback, it is considered that downsizing can be achieved by covering a periphery of an antenna element with ceramics having a high complex relative permittivity or by covering a periphery of an antenna element with a resin. The countermeasures take advantage of compression of a wavelength of an electromagnetic wave due to the high complex relative permittivity of the ceramics and the resin. However, in the case of covering the periphery of the antenna element with the ceramics, there are problems of high price and reduced resistance to impact. Also, since it is difficult to obtain a resin of high complex relative permittivity in the case of covering the periphery of the antenna element with the resin, there is a problem that satisfactory downsizing has not been achieved yet. Further, the high complex relative permittivity is considered to be achieved by mixing a magnetic powder with the resin. However, losses of inductive capacity and magnetism will be increased due to the magnetic powder, thereby undesirably causing deterioration in antenna characteristics.
This invention has been accomplished in view of the above-described circumstances, and an object thereof is to provide an ultrawideband communication antenna that is resistant to impact, reduced in losses, and satisfactorily small.